Early look at cotton insect outlook contains many unknown factors
Apr 7, 2004 12:00 PM, By Jack S. Bacheler North Carolina Extension Entomologist
Both producers and entomologists are far better at explaining insect pest outbreaks at the end of the growing season than at this time of year or even beyond the time of planting. Unfortunately, the timing and severity of our upcoming 2004 insect problems defy even a spring prediction.
Pest and beneficial insect survival during the winter, the abundance and quality of nearby crop and weed hosts during the spring and early summer months, the development of the cotton crop, and weather prior to and especially during the growing season, all affect insect levels.
In North Carolina all of our major insect pests undergo several generations on other hosts before moving into cotton. This makes early predictions even less reliable. Some observations, however, may be order.
(1.) Thrips have been rough for three of the past four years — 2000 to 2002 witnessed high thrips levels, while 2003 was very light in most areas of the state. Perhaps due to our cooler seedling grow off conditions, and the high ratio of surrounding weed and small grain thrips host vegetation compared with our small average field size, thrips levels are often higher and more damaging in the Carolinas and Virginia than elsewhere in the Cotton Belt.
Foliar treatment for thrips (approximately 55 to 75 percent of North Carolina's cotton acreage in 2000 through 2003 received one or more foliar applications for thrips), is often best timed when seedlings are difficult, though not impossible, to monitor — at the appearance of the first true leaf.
In this region, with the seed treatments Cruiser and Gaucho, plan on at least one foliar spray for thrips at the first true leaf stage. With the high thrips levels that are all too common here, consider the higher labeled rates for these foliar sprays.
With an at-planting treatment of Temik 15G (still the standard for thrips control in North Carolina), possible foliar sprays should be based on a combination of scouting for both damage to newly unfurling buds and leaves and live thrips.
(2.) Plant bugs will likely be kind to most producers in the pre-bloom period (we have averaged approximately 3-4 percent treated acreage over the past 5 years), but a possible headache in post-bloom Bollgard cotton, particularly in our far-eastern counties.
With our wet conditions and lush surrounding vegetation (good conditions for plant bug migration into cotton), 2003 was one of North Carolina's worst years for plant bugs.
Weekly square retention counts should define most potential problem fields up to about a week or two beyond bloom initiation. The crushing or cutting of quarter-sized bolls is probably best correlated with treatment need in the post bloom period for both plant bugs and stink bugs, although monitoring ‘dirty blooms’, visual observations for adult/nymph plant bug ratios, and sweepings are also helpful.
(3.) Stink bug damage has shown quite a lot of variability from one year to the next, with 2003 being a very light year for green and brown stink bugs overall. However, with more than 70 percent of our cotton acreage now planted to Bt varieties (including stacked Bt plus Roundup Ready lines), stink bug damage to cotton bolls has outnumbered bollworm damage by about 3:1, even with the single application of insecticide that producers average for late season insect control.
We need to be paying more attention to the bug complex in our Bt cotton. Additionally, when Bollgard II varieties become more widely planted in 2004, their expected lack of treatment for caterpillars will also result in greater potential buildups of bug pests.
Adequate sample sizes, lots of interior boll examinations, and green vs. brown adult ratios of stink bugs are a must in Bollgard fields. Fortunately, the three or so applications typically sprayed on conventional cotton keep stink bug and plant damage to bolls low.
(4.) Bollworm moth levels had seesawed up and down for the past 7 years here until 2003, when both 2002 and 2003 were rough bollworm years.
Our generally late-maturing cotton crop, coupled with an unusually extended bollworm flight, resulted in high bollworm damage to bolls in both Bollgard and in conventional cotton in several areas of the state in 2003.
An early high moth flight at the Rowland black light trap (in far southern North Carolina) often seems to signal a tough bollworm year for points north, while a later onset of the moth flight there is typically correlated with low bollworm years.
Counts from this trap and others throughout the cotton production area of North Carolina can be found on line at our project's Web page (www.run.to/cotton) beginning in early July.
(5.) Other caterpillars, such as fall and beet armyworms, European corn borers, and loopers have generally taken a welcome hike in recent years. Our wet 2003 appears to have shut down both beet and fall armyworms. Unlike its Bollgard predecessor, Bollgard II (currently available), and other upcoming Bt cottons such as VIP and Widestrike, all show high resistance to armyworms and loopers.
As always seems to be the case, upcoming weather patterns during the 2004 crop year will essentially dictate the timing and level of our potential insect problems — not to mention their influence on lint yield and quality.
Meteorologists, let alone us, have difficulty in predicting weather patterns (and their impact) more than about a week in advance. Fortunately, sound insect and plant monitoring and well-timed sprays where needed play a major role in making the best of what nature has in store for us this season.
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